【作者】 张莉；

【导师】 贾月梅；

【作者基本信息】 太原理工大学 ， 流体力学， 2010， 硕士

【摘要】 与柴油机相比,汽油机具有体积小、重量轻、噪音小、启动性能好等优点,在汽车行业得到了广泛地应用。然而由于汽车保有量的高速增长引发了环境污染和能源危机,迫切要求世界各国开展汽油机节能和降低排放方面的研究。进排气系统是发动机的重要组成部分,其内部气流组织的是否合理,不仅会影响发动机的动力性和经济性,而且会严重影响其排烟、排污、噪声以及工作的可靠性。要改进燃烧和降低污染,就必须对发动机的进排气系统进行深入、细致研究。由于实验条件的限制,单纯通过实验来研究发动机进气系统中气体的流动,不仅费用高而且实验周期长。而数值模拟方法具有资金投入少、周期短、仿真能力强、信息完全等优点,它基于流体力学和计算流体力学的基本理论,建立各种复杂条件下的守恒方程组,确定合适的定解条件,用数值计算方法直接求解这些联立的非线性偏微分方程组,从而得到整个流场中各变量的分布。本论文以某一型号汽油机的进排气系统为研究对象,对气道、气门以及气缸内的气体流动进行了仿真分析。首先用三维坐标仪对发动机的气道外形和气缸结构进行测量,然后用三维建模软件UG建立仿真计算所需的几何模型,对计算模型的划分采用动网格技术以及局部划分的非结构化网格技术,使网格变化与气道、气门及缸内的结构相适应。然后,通过阅览大量文献,确定基于有限体积法的计算方法及RNGκ?ε数学模型。最后用Fluent软件对发动机的进排气系统进行三维瞬态数值模拟研究,得到了其内部的压力场、速度场、湍动能场的分布。根据计算分析发现:1、在进气过程中,由于进气门并不是位于气缸的垂直中心线上,进气流动不均匀,并且在进气过程中进气门阻碍了气流进入气缸,进气门下方的空气被周围空气所卷吸,形成小涡,因此进气过程中产生了涡流现象。2、通过对进气过程中缸内横截面上速度矢量的变化分析发现,在接近气缸盖的截面产生的旋流最明显,其次是气缸中部,最后为接近活塞的地方。由此可以认为,气缸内产生的旋流是自上而下发展的,在接近活塞处慢慢消失。3、应用CFD对模拟结果进行分析评价,找出原结构中不合理的部位,提出改进方案,并再次进行数值模拟计算。结果发现:改进后的凹顶活塞结构顺应了气体的流动趋势,进气时气流的损失较小,无论是压力场、速度场还是湍动能场都得到改善。为今后汽车发动机进排气系统的CFD分析及结构优化研究奠定良好的基础,也能为实验装备的改进提供了一定的参考依据。更多还原

【Abstract】 Due to the light weight, low noise, and good starting performance, gasoline engine has been widely used in family cars. However the energy shortage and environment pollution has been becoming seriously, the fuel efficiency and reducing emissions are the objects pursued by researchers. Intake system is an important part of the engine,it will not only seriously affect the engine’s power performance, fuel economy, but also affect its exhaust emissions, vibration and the reliability. To improve the property of combustion and reduce pollution, research of air motion inside the system is necessary.As the restriction of the equipment in common use,the study on performance of intake system process only by experiment is not only long term, but also expensive. With the development of computer, numerical simulation plays is playing an increasingly important role, it has less capital investment, design and calculation speed, completeness of the information, the advantages of simulation capability. The numerical simulation is based on fluid dynamics and computational fluid dynamics. We set up a set of basic conserved equations in diversified complex conditions, then solve these simultaneous non-linearity partial-differential equations, and get the distribution of every variable in the whole flow field.In this paper, the situations of airflow inside gasoline engine were studied by numerical simulation. First, use three-dimensional equipment measured the engine’s shape, then use three-dimensional modeling software UG required to establish the geometric simulation model, divide the model by the unstructured grid. Secondly, analysis a large number of reference and determine the RNGκ?εturbulence model, finite volume method. Based on numerical methods, the pressure field, velocity field, and turbulent kinetic energy field were shown. The calculation results shows:1, The intake valve is not located in the center line of the vertical cylinder, during the intake process, air flows unevenly and the intake valve played a spoiler role, below the intake valve of the air is around air entrainment, and produced a vortex.2, Analysis the velocity vector cross the section when the different crank angle, it shows swirl generated by the cylinder is the top-down development, gradually disappeared near Detroit office.3, Through the analysis of the intake system, improved the scheme, and the numerical simulation. Found that improved the structure conform to the concave top piston gas flow trends in the intake air when the loss was small, whether it is the pressure, velocity, or the end of the turbulent kinetic energy field, and the results were slightly better in improving the former. The conclusions of this paper lay a good foundation for future analysis and structure optimization, but also provide a certain reference for the improvement of experiments.更多还原